This invention generally relates to an end shield structure for an electric motor or the like where the end shield includes a socket for mounting a cylindrical bearing, such as a ball bearing. More particularly, the invention is directed to such an end shield and its combination with other components where the socket is formed with integral one-piece construction allowing for automated assembly with minimum parts and with an improvement of quality.
Electric motors, and particularly fractional horsepower motors, must be of quality construction to give long service, and yet must be made efficiently and at low cost. Where cylindrical ball bearings are used to mount the rotor shaft, the alignment and concentricity of the bearing sockets is critical. Unlike "self-aligning bearings", the alignment of cylindrical roller bearings is determined by the sockets in which they are mounted. If the sockets are out of alignment, the bearings are out of alignment, and the life of the motor is severely shortened. Therefore, the mounts for cylindrical bearings must be precise as they retain the bearings radially and in axial alignment, and restrain them in the axial direction.
Another important consideration is that the rotor must be concentric with the stator to maintain a uniform air gap. Because the concentricity of the rotor is determined by the bearing sockets, these sockets must be precisely located.
The savings of labor and material are also crucial. This invention is specifically directed to a structure for accurately mounting cylindrical ball bearings in sockets formed in the end shields of the motor housing and where the sockets are of integral construction and may be formed with inexpensive operations using automated techniques.
Numerous structures have been used for forming sockets in end shields to support cylindrical bearings. These have included the separate fabrication of the sockets which are then secured to the end shields requiring extra labor and materials. Moreover, with such two piece construction it is difficult to accurately center the socket piece to achieve rotor and stator concentricity. The separate socket piece must be accurately centered and held in that position until secured by welding, rivets, or the like.
While integral structures are known for forming sockets for self-aligning bearings, such techniques have not been used for forming sockets for cylindrical bearings. For example, Hahndorf, et al. U.S. Pat. No. 3,391,290, Hoddy U.S. Pat. No. 3,529,874, and McGregor U.S. Pat. No. 4,428,688 each appear to disclose bearing sockets formed at least in part by the use of integral construction where the bearing socket is formed from the material of the end shield or the like. However, in each of these patents the socket is specifically for a self-aligning bearing where the bearing is allowed to align itself axially so that it may or may not be in axial alignment with the socket. In other words, there is no structure associated with the socket to align the bearing as the bearing aligns itself. Moreover, the socket of Hoddy does not appear to restrain the bearing in the axial direction.
In contrast to the sockets for self-aligning bearings as exemplified by the above referenced patents, in accordance with the present invention the integrally constructed sockets include structure that positively retain the bearings radially and in fixed axial alignment, and restrain the bearings in the axial direction. Generally, in accordance with the invention, the metal of the end shield is cut, such as by a punching operation, to define alternate ears and tabs. The ears are bent out of the plane of the end shield to extend at right angles thereto and define the cylindrical side wall of the socket. The inner surfaces of the ears are curved to generally conform to the cylindrical side of the bearing. The tabs are also bent out of the plane of the end shield to be outwardly offset from the plane but extend generally radially inwardly to define the end wall of the socket. The cylindrical bearing within the socket is retained radially and in fixed axial alignment by the cylindrical side wall of the socket, and is restrained in one axial direction by the end wall of the socket. While the cylindrical bearing mount of this invention contains the bearing, it permits axial movement within the restraints of the end walls so that the bearings may be preloaded, as is customary in ball bearing motors.
The sockets in the end shields at opposite ends of the motor housing are in axial alignment and are accurately centered so that the rotor and stator are concentric. At least one of the sockets may include within it a spring for resiliently preloading the bearings in the axial direction. The spring is located between the bearing and the end wall of the socket, and there may be included a washer or cap depending on whether an open or closed configuration is desired.
Therefore, it is a primary advantage of the present invention that the sockets for the cylindrical bearings are formed integrally with the end shield so that separate sockets and the additional labor and materials required to assemble them to the end shield are not required. The sockets accurately position the cylindrical bearings radially, and retain them in axial alignment. They also restrain the bearings axially, but allow them to move axially within the sockets within those restraints to provide preloading. The sockets may be formed with minimum labor and material loss by use of automated techniques.
These and other objects and advantages of the invention are apparent from the description to follow.